In recent years, major advances have been made in reducing the size of various electronic devices such as personal computers and personal digital assistants (PDAs), these advances primarily being the result of processor, memory and/or display improvements. Miniaturization of the keyboard, however, has proven to be a significant limiting factor in achieving further size reductions.
Several approaches have been pursued in overcoming the size reduction limitations imposed by the keyboard. First, many small devices, especially PDAs, do not use an integrated keyboard and instead offer a very limited set of input means (e.g., a few keys, thumb pad, small touch screen, etc.). Devices of this sort do not allow the user to input text by typing. Second, some devices that do not include an integrated keyboard may allow the use of a detachable keyboard. Such keyboards may utilize either full size or reduced size keys and may be foldable to allow easy portability. Third, expandable keyboards have been incorporated into laptop computers, thus allowing them to be relatively portable while providing the user with a full size keyboard during use. Fourth, miniature keyboards have been incorporated into handheld devices, providing the user with a full set of keys based on a standardized layout. The primary drawback of such miniature keyboards is that the user, while holding the device in both hands, types using only their thumbs, thereby eliminating the possibility of touch typing.
An approach that has been used in a variety of ways is the use of a reduced set of keys. For example, U.S. Pat. No. 6,011,554 discloses a keyboard in which multiple characters are assigned to each key. The keyboard is coupled to a disambiguating system which interprets keystroke sequences and provides the user with a list of words that match the keystroke sequence in question, preferably ordering the list by frequency of use.
U.S. Pat. No. 6,348,878 discloses a keyboard in which a primary and a secondary letter is assigned to each key. Striking a key causes the primary letter to be generated unless a secondary function key is also struck. The patent discloses designating the most commonly used letters as primary letters. Additionally, common two letter combinations are placed on primary mode keys proximate to one another.
Although the prior art devices allow a reduction in keyboard size, they also reduce typing efficiency by preventing the user from utilizing standard touch typing skills. Accordingly, what is needed in the art is a method and apparatus that allows a user to retain the benefits associated with touch typing while still providing a dramatically reduced keyboard. The present invention provides such a method and apparatus.